well.. there is, but it's not working while the client is running.
there are some dkp mods that show dkp listings of your members online. They usually use a launcher application that download a lua file from the guilds website into the addons folder and start wow after that.
the other way there are launcher that upload a savedvariables file after closing wow to a guild site to update e.g. profiles of the guild or a memberlist or something like that.
but as mentioned before there is no way to communicate in realtime with an external source.
Having to exit the client and parse lua is not a workable solution.
What I'm interested in is serializing an in game data structure (ace db for example) into an xml doc, presenting that data to the user in a text field or suitable component that can be copied into the clipboard, then alt-tab into another app to paste the data (like a webform). So - while it is not interprocess communication, it is a more effective means of exchanging data between the game and external apps because the client does not need to halt. I am also looking for the opposite, where xml is generated externally and parsed via lua into a live client. I've used some mods (ct_raidtracker modded, raidbanker) that go in-game->xml text->web form, but none of them are ace. I'm wondering if an Ace solution to this has been developed, but it doesnt look like it.
Character profile generation. Parse the character into an xml document, then load that profile onto the guild website.
Guild roster management. Parse the guild roster into an xml document. Load it into a web form. Change the guild roster as desired. Generate a changes xml document. Bring that back into the game and perform the changes w/ UI confirmation.
To be frank, making the user copy/paste raw code is almost as much hastle as having them relog... and users much prefer purdy simple interfaces with single "update" buttons over copy/pasting mysterious jibberish...
But that's not to say it's not possible. But here amongst the Aceholes we've had no need for external comm of any sort, yet, so we don't really have any examples or standards amongst us.